1. Field of the Invention
The present invention relates to an electron microscope which observes the micro-action of a fracture or deformation of materials such as metal, ceramics, etc. More precisely, it relates to an improved electron microscope by which a sample at a temperature higher than 800.degree. C. can be observed.
2. Description of the Related Arts
In the conventional scanning electron microscope, an electron beam is radiated on the sample, and then secondary electrons are generated from the sample which are attracted to a photo multiplier, and via a photo multiplier tube, displayed on a screen of a cathode ray tube.
In the above-mentioned conventional electron microscope, the resolution at a high temperature is poor. This reduction of resolution is considered to occur because, in addition to the secondary electrons generated from the sample to be observed, thermal electrons are also generated from the sample or the heater coil and combine with the secondary electrons to cause a disturbance of the cathode ray tube image. Also, a disturbance is caused when the heater coils are wound in the same direction. Particularly, this phenomenon is greatly enlarged when the sample is heated above 800.degree. C., seriously affecting the reliability of the data obtained.